The objective of this proposed research is to define, in molecular terms, the mechanisms that control the expression of herpes simplex virus (HSV) genes in transformed cells. The proposed studies center on the expression of HSV thymidine kinase (TK) in biochemically transformed cells. In particular, we are interested in studying the relationship between information content and expression. This will be done by making available to mouse Ltk- cells various length restriction endonuclease generated fragments of HSV-1 DNA that contain the TK gene. Cells that have stably acquired the TK ion phenotype will then be examined for viral DNA sequences, and transcripts from the now resident viral DNA.